In a large number of mobile storage systems, the mobile storage units are selectively movable along rails to which the units are mounted. The units can be moved on the rails in a manually operated manner, or through the use of a motor, such as an electric motor operably connected to wheels that move the storage unit along the rails. In such motor-powered units, the user selectively actuates a switch to operate the motor, and a drive system between the motor output shaft and the wheels is operable to rotate the wheels in order to move the unit along the rails in the desired direction.
When a storage system including a number of mobile units is employed, once the units are loaded, the floor or other surface underlying the rails tends to deflect under the weight of the storage units and the items loaded in each unit. This deflection of the floor or other underlying surface causes deflection of the rails, which creates a curved rail profile defining a lowermost point between the opposite ends of the rails. As a consequence, the wheels of each storage unit have a tendency to move along the rails under the influence of gravity toward the lowermost point of the rails. Thus, when the motor of each storage unit is not being operated to move the storage unit along the rails, the rotational tendency of the wheels causes the unit to drift from the stationary position away from the desired position toward the lowermost point of the rails caused by deflection of the floor or other underlying surface. To prevent this, a number of different locking mechanisms have been developed which engage adjacent storage units with one another and/or with stops or end panels positioned at each end of the storage system to prevent the inadvertent or unintended movement of the units in response to deflection of the rails. However, such locking mechanisms normally require a number of additional components to be integrated into each unit of the storage system, which increases the overall complexity and cost of the each unit, and for the overall mobile storage system. Furthermore, such locking mechanisms are often manually operated, and therefore require an individual to actively engage the locking mechanism in order to prevent the movement of the movement of the units with respect to one another.
Therefore, it is desirable to develop a storage system that prevents inadvertent or unintended movement of the storage units when the storage units are placed in a desired position. It is further desirable to provide a storage system that includes a number of motor-driven storage units, and which includes an automatically operated locking or braking mechanism that holds each storage unit in a desired location when the motor is not being operated to move the storage unit. The locking or braking mechanism should be automatically engageable when operation of the motor is stopped, and should have a minimum number of components to reduce cost and the facilitate incorporation into both new and existing storage units.